The main method for estimating wettability of a solid surface with two immiscible liquids is the method of studying a contact angle formed by phase interface with the solid surface (see, for example, U.S. Pat. No. 7,952,698).
The main disadvantages of the known method are a long time needed for achieving the equilibrium contact angle (up to 1000 hours), contact angle hysteresis caused by different reasons such as heterogeneous structure of the surface, surface irregularities, etc. Another serious disadvantage of this method is that the said method can be applied to smooth flat surfaces only and adaptation of this method to measurement in porous media is rather difficult and in some case is impossible at all. For example, in oil and gas industry, rather than the method of contact angle study, petrophysical investigations of rock core samples are used for determining wettability of porous media. It is in a small number of cases, with a pronounced character of wettability, that wettability can be estimated by results of other methods of investigations. In petrophysical investigations of rock cores, the Amott's method is mainly used (E. Amott, “Observations Relating to the Wettability of Porous Media,” Trans, AIME, 216, 156-162, 1959) or its modifications: the Amott-Harvey and USBM methods (see, for example, J. C. Trantham, R. L. Clampitt, “Determination of Oil Saturation After Waterflooding in an Oil-Wet Reservoir—The North Burbank Unit, Tract 97 Project,” JPT, 491-500 (1977)).
All of these methods simulate a process of oil production from a reservoir and are based on successive substitution of oil for a mineral solution or a mineral solution for oil through natural or forced (by means of centrifugation) imbibitions of a sample with measurement of saturation with fluids. All of the above-listed methods are indirect methods of investigation and provide no accurate thermodynamic information about such thermodynamic characteristic as wettability. Another disadvantage of these methods is their low sensitivity in the area of neutral wettability or with small dimensions of a sample.
In recent years, the method of wettability determination based on calorimetric measurements of wetting heat is being actively developed. Investigations of wettability in a system solid—liquid—gas (saturated vapor of this fluid) were conducted (see, for example, R. Denoyel, I. Beurroies, B. Lefevre, “Thermodynamics of wetting: information brought by microcalorimetry,” J. of Petr. Sci. and Eng., 45, 203-212, 2004). Among advantages of this method, one can mention high accuracy of wettability estimation based on thermodynamic measurements, among disadvantages—a low sensitivity in case of small accessibility of sample surface.
Wetting heat can also be used for determining a surface area of a sample with the use of the modified Harkins-Jura method (Partyka S., Rouquerol F., Rouquerol J. “Calorimetric determination of surface areas: possibilities of a modified Harkins and Jura procedures.” Journal of colloid and interface science, Vol. 68, No. 1, January 1979).
For measurement of adsorption heat, various calorimetric cells may be used. Glass or metal cells are most often used. Before an experiment, a surface of a sample is cleaned by means of evacuation under the effect of increased temperature. In the process of examining adsorption heat, vapor of a liquid under examination is supplied into a cell under controlled pressure and after that heat of adsorption is measured.
For measurement of wetting heat, various types of calorimeter measuring cells are used. Most often, a pressure tight cell is used inside which a sample closed in a sealed glass balloon is placed (see, for example, R. Denoyel, I. Beurroies, B. Lefevre, “Thermodynamics of wetting: information brought by microcalorimetry,” J. of Petr. Sci. and Eng., 45, 203-212, 2004). The balloon with the sample is previously evacuated and sealed off, that making it possible to obtained a controllable state of sample surface before the experiment. When conducting the experiment, the balloon is broken and the sample is wetted with the liquid. A membrane cell is a cell divided by a membrane, as a rule made of metal, into two parts. The sample is placed into a lower part and the liquid—into an upper one. In the process of experiment, the membrane is cut and the liquid flows into the lower part of the cell. The advantage of this type of cell is that in this case no sealing of the sample in a glass balloon is needed; the disadvantage is that the sample in this case is not evacuated, which may result in serious measurement errors for wetting heat. In yet another version, a cell merges advantages of the two above-described designs (see, for example, P. N. Aukett “A new membrane cell for the determination of heats of immersion using the Setaram c-80 microcalorimeter” Journal of Thermal Analysis, Vol. 33, 323-327, 1988). The liquid and the sample are separated by a membrane, while the lower part of the cell has a vacuum lock and can be evacuated before the experiment. The disadvantage of all of the above-mentioned cells is impossibility to control pressure during the experiment because the cells are not connected with other parts of the setup by means of tube connections. In such cells, it is difficult, if not impossible, to conduct experiments under increased pressures.
In the work (R. Denoyel, I. Beurroies, B. Lefevre, “Thermodynamics of wetting: information brought by microcalorimetry,” J. of Petr. Sci. and Eng., 45, 203-212, 2004), it is proposed to utilize for measurement of wetting heat an apparatus in which pressure in a cell can be controlled. The measuring cell, via tubular connections, is connected via a T-adapter with a vacuum pump on the one side, which makes it possible to evacuate the sample before the experiment, and on the other side with a system that makes it possible to supply the liquid to the cell and to create pressure of this liquid in the cell. It should be noted that the liquid supplied into the cell should have a temperature close to the temperature in the measuring system in order not to create an additional heat flow rendering difficult the wetting heat measurement.
For each of the proposed configurations, it is necessary to account for additional thermal effects appearing in the process of experiment that are connected with breaking a balloon or rupture of a membrane, a thermal effect appearing as a result of temperature difference between the liquid entering into the cell and temperature of the cell, thermal effect associated with compressing of the liquid in the cell (when increasing pressure to the required level), etc. These thermal effects, as a rule, can be accounted for through conducting additional measurements.